Mobile home underframe

ABSTRACT

An underframe structure, system and method for use with mobile homes and other transportable buildings including a pair of longitudinal beams made of C-sections, an interlocking C-section used at the area of greatest bending moment, a reinforcing hatsection member rigidly affixed to each beam but removable therefrom to increase stiffness in the area of greatest bending moment, a wheel support structure depending from the hat-section member, and a removable hitch on the underframe which can be attached to the wheel support structure and hat-section members to move them independently of the underframe. The disclosure also includes a method of assembly of such an underframe structure, using a minimum of simple jigs. There is also disclosed a method for moving a mobile building from a first location to another location wherein a wheel support structure which includes elongate stiffening members is mounted beneath the building in such a way as to improve the stiffness of the building underframe during transporting, a removable hitch member is attached to the frame of the building, the building is moved to the other location, and the support structure and hitch are then removed from the mobile building and attached to each other for transportation independently of the building, while the building is lowered to a suitable foundation.

United States Patent n 1 Goodson, Jr.

1 MOBILE HOME UNDERFRAME [75] Inventor: Albert A. Goodson, Jr., Houston,

Tex.

[73] Assignee: Southwestern Pipe, Inc., Houston,

Tex.

[22] Filed: Dec. 8, 1971 [21] Appl. No.: 205,892

[52] U.S. Cl. 280/106 T, 214/1 H, 280/30 [51] Int. Cl 860p 3/00 {58]Field of Search 214/1 H, 515,152;

280/106 T, 34 A, 30, 80 B; 296/23 R; 52/143 [56] References Cited UNlTEDSTATES PATENTS 3,254,914 6/1966 Steck 296/28 R 3,317,219 5/1967 Hindinet al. 280/80 B X 3,365,211 1/1968 Ginsburg 280/80 B 3,664,082 5/1972Zintel...'..... I 52/143 X 3,092,396 6/1963 Thomas 280/106 T FOREIGNPATENTS OR APPLlCATlONS 1,562,963 3/1969 France 52/143 PrimaryExaminerGerald M. Forlenza Assistant Examiner-'Frank E. WernerAttorney-Ned L. Conley et a1.

[57] ABSTRACT An underframe structure, system and method for use withmobile homes and other transportable buildings including a pair oflongitudinal beams made of C- sections, an interlocking C-section' usedat the area of greatest bending moment, a reinforcing hat-section memberrigidly affixed to each beam but removable therefrom to increasestiffness in the area of greatest bending moment, a wheel supportstructure depending from the hat-section member, and a removable hitchon the underframe which can be attached to the wheel support structureand hat-section members to move them independently of the underframe.The disclosure also includes a method of assembly of such an underframestructure, using a minimum of simple jigs. There is also disclosed amethod for moving a mobile building from a first location to anotherlocation wherein a wheel support structure which includes elongatestiffening members is mounted beneath the building in such a way as toimprove the stiffness of the building underframe during transporting, aremovable hitch member is attached to the frame of the building, thebuilding is moved to the other location, and the support structure andhitch are. then removed from the mobile building and attached to eachother for transportation independently of the building, while thebuilding is lowered to a suitable foundation, 1

7 Claims, Drawing Figures PAIENIED AUG 7 I975 SHEHIBFS INVENTOR. A/berfA. 6000000, 47/:

PATENIED SHEEI 20F 3 INVENTOR. A/berf A. 600G000, (fr.

1 MOBILE HOME UNDERFRAME BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates to underframe systems for portablebuildings and to methods for moving portable buildings from one locationto another.

2. Description of the Prior Art Portable buildings, such as mobilehomes, are designed to be towed from one location to another andpositionedmore or less permanently at the second location. In most casesthey are not thereafter moved to another location. It has been thepractice to provide such portable buildings with an underframe made ofsteel beams which has a hitch at one end for connection to the towingvehicle and one or more pairs of wheels beneath the frame at a distancefrom the hitch of about two-thirds of the length of the building. Thewheels are thus positioned so that they bear a major portion of the loadand only a minor portion is carried on the towing vehicle. Such anarrangement is described, for example, in U.S. Pat. No. 3,276,790 toMcKaig.

In order to reduce the cost of such structures it has been proposed tomake the wheels and hitch removable so that once'the portable buildinghas been transported to the destination these elements can be removed,and the hitch used to tow the wheel structure back to the factory ordealer. Designs for this purpose are shown, for example, in U. S. PatNo. 3,254,914 to Steck and U.S. Pat. No. 3,505,767 to Fyle, Jr,

A major problem in the transporting of mobile homes and other portablebuildings in this manner has been that the underframes are not stiffenough to prevent distortion under the load of the structure of thebuilding and furniture or equipment within the building. Thus it hasbeen found, in one study, that the underframe is responsible for onlyabout 15 per cent of the total stiffness (ratio of applied load todeflection) of a mobile home on the longitudinal direction. Theremainder of the stiffness is provided by the side walls and theexterior covering on the walls See the reports of Batelle MemorialInstitute entitled Design Improvements in Mobile Homes With NewApplications of Steel" rendered to United States Steel Corporation onMar. 17, 1967 and Jan. 31, 1968. These reports point out that because ofthe high proportion of the load carried by the wall structure the wallsare subject to bending and buckling during transportation of the mobilehome.

In many designs the poor connection between the frame and the side wallsprevents depending on the side walls for supporting any of the floorload between the wheels and thehitch. In such installations the framehas to be designed to carry up to 75 percent of the total load(everything except the walls and the roof), during transportation of thehome, to prevent tearing the frame and floor structure loose from thewalls.

It has heretofore been proposed to add reinforcing structure to a framemember in areas of high load to decrease deflection of the frame memberin such areas and thereby provide greater stiffness of the member.However, such additions of reinforcing means have been consideredobjectionable in the case of mobile homes and other portable buildingsbecause of the increased weight and cost of an element which is requiredonly during the relatively short period of transporting the buildingfrom one location to another.

SUMMARY OF THE INVENTION The present invention provides an underframeand support structure for portable buildings and the like wherein" thearea most subjectto deflection during transporting of the building issubstantially strengthened for transporting, but wherein thestrengthening structure is removed at the destination and can be reusedin the transporting of additional structures. In one embodiment of theinvention the underframe structure is substantially strengthened atareas of maximum stress by elements which are not removable.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a foreshortened plan view ofan underframe according to one embodiment of this invention;

FIG. 2 is a longitudinal sectional view of the embodiment of FIG. 1,taken at line 22 of FIG. 1;

FIG. 3 is a transverse half-sectional view of the embodiment of FIG. 1taken at line 3-3 of FIG. 2;

FIG. 4 is a sectional view of one element of the embodiment shown inFIG. 1, taken at line 4-4 of FIG.

FIG. Sis a sectional view of one element of the embodiment shown in FIG.1, taken at line 5 5 of FIG.

3; FIG. 6 is a generalized moment diagram showing the bending momentslongitudinally of an underframe of the embodiment shown in FIG. 1;

FIG. 7 is an elevational view of a subassembly of the embodiment shownin FIG. 1;

FIG. 8 is a'plan view of the embodiment'of FIG. 1, shown in anintermediate stage of construction; and

FIG. 9 is a sectional view taken at line 9-9of FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS v The underframe shown in thedrawing generally comprises a pair of parallel spaced apartlongitudinally extending beams 10, each of which, in the embodimentshown, is made upv of a main beam 12 and reinforcing beam 14 which issubstantially shorter than the beam 12 and extends along an intermediateportion thereof, preferably being tackwelded to it so that the two beamsfunction as a unit. Connecting cross beams 16 extend between the twomain beams and outriggers 18 extend laterally outwardly from each mainbeam generally aligned with the cross beams 16. Cross beams 16 andoutriggers 18 are preferably welded to the main beams. A front end beam20 closes the front end of the underframe and a rear end beam 22 closesthe rear end of the frame. A hitch assembly 24 is provided at the frontend of the underframe for connection to a towing vehicle.

In the preferred embodiment of the invention the main beam 12 and thereinforcing beam 14 are each C- section members having substantiallyindentical web and flange dimensions which are interlocked with eachother as shown in FIG. 3, with the upper, narrower flange of beam 14being contained within the upper flange of beam 12 while the lowerflange of beam 12 rests within the lower wider flange of beam 14, andwith the outside lip of each beam welded to the web of the other beam.The two beams may be of different wall thicknesses, but otherwise arepreferably of substantially the same dimensions in cross section.Preferably they are cold rolled from sheet steel for ease in fabricationand to insure uniformity and strength Such structures are known in theprior art for use inconstruction. If desired, the two beams may be spotwelded together to improve their ability to act as a unit. In someembodiments of the invention, however, it may be desirable to omit beam14 altogether.

In the embodiment shown the cross beams 16 and 16A and the end beams 20and 22 are channel members which may also be cold rolled from sheetsteel. In this embodiment the outriggers 18 are Z-shaped members. Thecross beams and outriggers are attached to the longitudinal beams as bywelding, with a short piece of C-section member 26 interlocked with themain beam 12 at the point of attachment of each cross member USA whichdoes not intersect the reinforcing beam 14. As shown in FIGS. 3 and 4the outriggers 18 are fastened with a slight upward camber, i.e. theouter end is higher than the end attached to the longitudinal beam. Thepurpose of this is to compensate for deflection which occurs as a resultof the weight added when the wall structure is erected.

In addition the beams 10 may also be provided with initial camber, asshown with reference to the horizontal reference line 27 in FIG. 2. Suchcamber can be provided in the rolling of the beams 12, so that forexample the rear end of beam 12 may be two to three inches higher thanthe portion of the beam directly over the wheels, and the portion of thebeam between the wheels and the hitch carried curved upwardly and thendownwardly, asshown for example in exaggerated form in FIG. 6 of thedrawing. Thus, in this embodiment the main frame as rolled is in crosssection in the form of an ogee. This curvature compensates fordeflection which occurs due to the weight added when the floor and wallstructure are built onto the underframe, so that when the mobile homestructure is'completed the underframe will be substantially straight.

Alternatively, the camber may be provided after the underframe isassembled on the wheels, by first lifting at the rear end-(the right endas shown in the drawing) and heating the upper surface of the beams 10until the weight of the wheels causes the beam to sag the desiredamount, and then putting a support between the wheels and the front end,pressing down on the front end, and heating the bottom of the beam.

According to this invention the hitch 24 comprises a V-shaped member 28having a flange 30 welded on each leg and a pair of diagnonal members 32extending in alignment with the V-shaped member to intersect theparallel beam members 12. The diagonal members 32 are welded to theshort C-shaped sections 26 and to flanges 34 attheir opposite ends,which are received within the end cross member 20. The flanges 34strengthen the cross member 20 at the point where the hitch is attached.Aligned bolt holes are provided through the corresponding flanges 30 and34 and the web of the cross beam 20 for receiving bolts 36 by means ofwhich the hitch element 28 is removably fastened to the underframe.

Removable support assembly is provided for use during construction andwhile transporting the underframe from one location to another, suchsupport assembly comprising a pair of longitudinally extending channelshaped members 38 having their webs lying flat against and extendinglongitudinally of the lower flange of the longitudinal beams 10, andbeing ridigly but removably fastened thereto by means of bolts 40. Thefastening is such that the channel shaped members 38 are held in tightengagement with the beams 10 so that each combined beam and channelmember acts as a composite structural member, i.e. there issubstantially no slippage between them, and structurally they act as asingle unit. Because of this, the amount of stiffness added by theaddition of mmbers 38 is two to three times as great as the stiffness ofthe members 38 alone. Preferably the channel shaped member has, as shownin the drawing, a hat shaped cross section, i.e., has a lip on eachflange extending outwardly. Since the lower edge of this memher is undercompression the outwardly extending lip on each side increases theresistance to buckling of the member.

The members 38 are provided with a plurality of spring shackles 42 whichmay, for example, be welded thereto to receive the ends of springs 44which are mounted in a conventional manner on axles 46, which in turnsupport one or more pairs of wheels 48. The usual pivoting links and thelike may be used to allow functioning of the springs.

For ease in assembly, the nuts into which bolts 38 are received may bewelded over bolt holes cut in the lower flange of beams 12 and 14,andhat-section member 38 may have corresponding holes in its web.

Although two axles are shown in the drawing, one axle is sometimes used,and larger mobile homes may have three or more.

In theconstruction of an underframe. according to the present inventionthe longitudinal beams, cross beams and outriggers are assembled in ajig, with welded connections being made therebetween'as previouslydescribed herein. The hitch elements are also assembled onto theunderframe. In those underframes which utilize the reinforcing beam 14interlocked with the main beam 12, the lower flange of beam 12 must havesuitable holes punched and nuts welded on to receive the bolts 40 whichare utilized to bolt on the channel member 38.

The support assembly may be assembled separately from the underframestructure and the underframe structure then lifted onto the supportassembly and connected as by means of the bolts 40. The combinedassembly may then be towed to the next stage of assembly, where theusual floor joists and flooring is attached. The weight of this materialis enough to counteract the camber which was rolled into the beams 10 sothat once the floor has been assembled onto the underframe the beams 10are straight and level. Wall sections may then be mounted on the floorstructure. As

previously noted herein, the wall sections'are stiff enoughtosupportthemselves and the roof so that the weight of these sections does notcause undesirable deflection of the underframe.

In a preferred embodiment of the invention, the cross beams 16A areassembled on to the short segments of C-section material 26 as shown inFIG. 7, the end of the cross beams being welded to the pieces ofC-section. As shown in the drawing, the ends of the cross beams 16A arenotched at the top at 60 to provide clearance for the upper lips of thelongitudinal beams 12.

For assembly, the longitudinal beam members 12 are preferably supportedat a good working height on supports 70, which preferably are adjustablein height,- as by means of scissor jacks or the like, so that the beams12 may be levelled. When the beams 12 are laid in place the assembliesof cross beams 16A and members 26 may be inserted by twisting slightlyso that the upper flanges of the members 26 slip within the beams 12 andthe welded assembly can then be lifted upwardly to interlock theC-sections, as shown in FIG. 9. Clamps may be applied to hold thesepieces in place. This provides rigid positioning of the two beams 12with respect to each other and accurately locates them at the properdistance apart. When all of the cross beams of 16A are assembled in thismanner, they may be welded in place.

Other cross beams 16 may then be welded in place and the outriggers andthe hitch structure attached as shown in the drawings. The wheelassembly may then be bolted in place, the adjustable supports lowered tolower the frame on to the wheel assembly, and the entire underframeassembly may be towed away. When the assembly of the structure has beencompleted it may be removed from the support structure for storage orfor transportation by rail or other means, or it may be left on thewheel support structure and towed to the destination selected. Uponarrival at the destination the mobile home or other portable bulding maybe jacked up, the bolts 40 removed, and the wheel support structuremoved from beneath the mobile home. The bolts 36 may then be removed sothat the hitch 24 can be taken off the front end. An adapter member (notshown) may then be bolted between the channel members 38 and the hitchmember 24 bolted thereto for towing the wheel assembly back to thefactory or dealer.

The mobile home may then be lowered to rest on a concrete slab or othersuitable foundation. Preferably the beams will rest flat on a flat slab,and brackets welded or bolted to the beams 10 (not shown herein) may beused to bolt the underframe to the concrete slab, thereby providingsubstantial resistance to overturning of the mobile home by high winds.

When the center of the wheel support structure is approximatelytwo-thirds of the length of the mobile home from the hitch point,assuming a substantially uniform load throughout the length of themobile home, the maximum bending moment on the underframe is at thecenter of the wheel support structure and is approximately twice thebending moment at the next highest point which is roughly one-fourth ofthe length of the underframe from the hitch connection. This isillustrated in FIG. 7 of the drawing where the highest bending moment isshown at M and the next highest bending moment is shown at M,. In orderto insure adequate support between the wheel support structure and thehitch the beam 12 is designed with sufficient stiffness that, combinedwith the stiffness provided with the side wall, adequate resistance todeflection from the moment M, can be provided. it is apparent, however,that if the beam is designed so that it has only enough stiffness toresist M it will deflect too much at the areas of greater bendingmoment. Such deflection is prevented in the preferred embodiment of thisinvention by including the reinforcing beam 14, which extends over adistance encompassing all of the area of greater bending moment, andwhich provides a substantial degree of greater stiffness to thisportion. The channel-shaped member 38, which may have the same length orbe shorter than reinforcing beam 14, then provides additional strengthin the area of highest bending moment.

In some installations, the increased resistance to bending in the areaof highest bending moment may be provided by the hat-section members 38alone, so that the reinforcing beams 14 are not required.

However, when the mobile home has been moved to its final resting placethis stiffness to resist M, is not required, since when placed on afoundation the underframe will be supported at numerous points along itslength, and preferably will be supported throughout its length, so thatthere will be no concentrated bending moment such as exists duringtransportation of the mobile home.

One of the principal advantages of the use of the interlockingC-sections is the fact that identical C- sections may be used for themain beams and the reinforcing beams. However, if additional strength isrequired, it is only necessary to roll one or the other of the beamsfrom a thicker gauge material. Thus, addi- 1 tional strength can beadded without adding to the bulk of the beams.

Another advantage of the interlocking C-sections is that they arereadily interlocked with each other, since they are easily assembledtogether without sliding one down the length of the other. Such sectionsare also advantageous as compared to channels because the net depth (webwidth) required for a particular load is reduced by the amount of thereturn lip In other words, fora corresponding channel to have the samestrength it would have to be higher. Thus, the use of a C-section, asopposed to a channel, allows a reduction in the overall height of theunderframe, thereby lowering the overall height of the mobile home.This, plus the removal of the wheel support structure and otherframe'mernbers beneath the main beams 10, allows the mobile home to beset lower to the ground, thereby in many cases eliminating the need forsteps for entry into the mobile home, and facilitating enclosing theunderframe for better insulation of the floor.

' Thus, according to this invention there has been provided anunderframe structure for a mobile home or other portable building whichis adequate to provide full support for the building during transportingfrom one location to another, and which includes a reinforcing structurewhich is attached to the underframe in such a way as to form an integralpart of the support structure during transporting, thereby providing theadditional stifl'ness required to counteract the high bending momentpresent over the wheels, but which support structure is removable uponarriving at the destination, when such additional stiffness is no longerneeded.

Although preferred embodiments of the invention have been shown anddescribed herein, the invention is not limited to these embodiments butonly to those which are within the scope of the accompanying claims.

I claim: 1. A support frame comprising a pair of parallel spaced-apartbeams, a plurality of cross-members secured therebetween,

and asupport structure connected to said beams to support said beamsalong at least one line traversing said beams intermediate their ends,whereby the bending moment on'said beams atand adjacent along the lengthof the. beams, each of said beams comprising a C-section with its weblying in the vertical plane, said Csection having upper and lowerflanges of different widths,

a second C-section having substantially identical web width and flangewidths interlocked with the first C-section with the narrower flange ofeach C-section nesting within the wider flange of the other C-section,said second C-section extending a length encompassing a substantialportion of the area of substantially greater bending moment butsubstantially less than the length of the first C-section.

2. A support frame as defined by claim 1 wherein the lip of theexteriorly disposed flange of each C- section is welded to the web ofthe other C-section. 3. A support frame as defined by claim 1 andincludmg a channel shaped member affixed to the lowermost flange of eachbeam to depend therebelow and extending longitudinally of the beam for alength encompassing a substantial portion of the area of substantiallygreater bending moment. 4. A support frame as defined by claim 3 whereinsaid channel-shaped member is hat-shaped.

5. A support frame as defined by claim 3 wherein the support structureis connected. to the channelthe channel-shaped members are removablyattached to the beams.

* 1R I i

1. A support frame comprising a pair of parallel spaced-apart beams, aplurality of cross-members secured therebetween, and a support structureconnected to said beams to support said beams along at least one linetraversing said beams intermediate their ends, whereby the bendingmoment on said beams at and adjacent said line is substantially greaterthan at other points along the length of the beams, each of said beamscomprising a C-section with its web lying in the vertical plane, saidCsection having upper and lower flanges of different widths, a secondC-section having substantially identical web width and flange widthsinterlocked with the first C-section with the narrower flange of eachC-section nesting within the wider flange of the other C-section, saidsecond C-section extending a length encompassing a substantial portionof the area of substantially greater bending moment but substantiallyless than the length of the first C-section.
 2. A support frame asdefined by claim 1 wherein the lip of the exteriorly disposed flange ofeach C-section is welded to the web of the other C-section.
 3. A supportframe as defined by claim 1 and including a channel-shaped memberaffixed to the lowermost flange of each beam to depend therebelow andextending longitudinally of the beam for a length encompassing asubstantial portion of the area of substantially greater bending moment.4. A support frame as defined by claim 3 wherein said channel-shapedmember is hat-shaped.
 5. A support frame as defined by claim 3 whereinthe support structure is connected to the channel-shaped members,whereby the support frame is supported through the channel-shapedmembers.
 6. A support frame as defined by claim 5, wherein the supportstructure comprises a pair of wheels mounted on an axle, and the axle ismounted on leaf springs, the ends of which are secured to thechannel-shaped members.
 7. A support frame as defined by claim 5 whereinthe channel-shaped members are removably attached to the beams.